The introduction of digital video recorders makes it possible to record conventional video signals which, for example, meet the CCIR 601 standard in a digital format. It is thus possible to digitally record video signals and to reproduce them in the identical format.
By using a standardized video recording device it is thus possible to mix program material of different standards and to record it in one standard. For example, one video signal can be provided from a camera which supplies a progressively scanned video signal with 625 lines and a picture frequency of 50 Hz, and a second signal from another source can be a standard line interlaced video signal with 625 lines and a picture frequency of 50 Hz.
A recording device according to the CCIR 601 standard, for example, can record only line interlaced video signals and is characterized by a limited band width. Thus it is necessary to reduce the data rate of a progressively sampled video signal, and to convert the signal to a line interlaced video signal. Data reduction can be performed, for example, by filtering. The generation of a line interlaced video signal can, for example, be performed in connection with such filtering by means of a so-called line shuffling technique. A video signal so obtained constitutes a signal according to the CCIR 601 standard and therefore can be recorded. Post-processing by means of inverse line shuffling and inverse filtering can be employed to enhance the reproduction of the original progressive video signal image.
U.S. Pat. No. 4,652,909 and H. Sauerberger, "Breit und Schmalbandige Kompatible Einkanalige HDTV-Ubertragung (Compatible Single Channel HDTV Transmission with Wide and Narrow Bands)", Fernseh-und Kinotechnik No. 1/2 1987, discuss how progressively scanned video signals are filtered, subsampled and provided with artificial line interlacing so that they can be transmitted via standard television channels. U.S. Pat. No. 4,652,909 also describes how such signals can be recorded or reproduced.
The original progressive video signals with artificial interlacing can also be mixed with standard video signals and recorded, for example, after such preprocessing. Combined signals so generated are also subjected to post-processing for reproduction enhancement. However, in doing this the recorded standard video signals are also post-processed upon playback, resulting in visible image distortion associated with these signals. U.S. Pat. No. 4,652,909 and the Sauerburger article do not address the problems resulting from such processing of video signals, and offer no solution for such problems.
It is an object of the invention to provide a picture processing system which is able to mix, record and reproduce television signals of different standards, and to avoid errors associated with post-processing.